Forced to apologise to patients last week just 24 hours after claiming the National Health Service was not in crisis, the controversy forms an unwelcome backdrop to Mrs May’s first wide-ranging reshuffle since becoming Prime Minister in July 2016 – and whether to promote, among others, Health Secretary Jeremy Hunt.

Though she carried out limited changes after last June’s election, and then the resignations of Sir Michael Fallon and Priti Patel, the Tory leader clearly feels emboldened after successfully concluding the first phase of Brexit negotiations last month. “I’m not a quitter. I’m in this for the long term,” she declared.

Asked if she would lead the Tories into the next election, due to be held in 2022, she replied: “Obviously I serve as long as people want me to serve.”

Yet Mrs May’s careful choice of words reflects the invidiousness of her position after losing her Commons majority – her party has been unable to coalesce around an alternative leader.

And, while she will have been relieved that her first interrogation of 2018 was not dominated by Brexit, mounting concerns about the delivery of domestic reforms – including the NHS – have prompted her to choose this moment to freshen up her top team.

Although Mrs May spent the past week in her Maidenhead constituency – the interview was pre-recorded at a local hotel – she travelled to nearby Wokingham to promote new housing policies before making the short trip to Frimley Park Hospital in Camberley to meet doctors.

She has remained in constant touch with close aides including the Skipton and Ripon MP Julian Smith who, as Chief Whip, is advising the Prime Minister on the Cabinet changes that are open to her without further destabilising the Government.

However, Mrs May chose to go on the political offensive over the NHS. She firstly reiterated her claim that the NHS has never been better prepared for this year’s winter pressures and postponing 55,000 operations was “part of the plan”.

“Of course we want to ensure that those operations can be reinstated as soon as possible, but it’s about making sure that those who most urgently need care are able to get that treatment when they need it,” she said.

Mr Marr raised the case of a 72-year-old stroke victim who waited in an ambulance for an hour, and a further four hours in a hospital in Chelmsford, before she saw a doctor.

He said: “If I’d been waiting for five hours before I’d seen a doctor after my stroke I would not be here talking to you.

“This is about life and death and up and down the country people are having horrendous experiences of the NHS.”

Mrs May did not comment on the individual case, but said: “If we look at what is happening across the NHS, what we see is that actually the NHS is delivering for more people, it is treating more people and more people are being seen within the four hours every day than has been a few years ago.

“But of course nothing’s perfect and there is more for us to do.”

On funding, it was suggested to Mrs May that she had done nothing to address increased pressure on the social care system.

She said: “We have put extra funding into the social care system and we have worked with hospitals and with local authorities to identify how we can reduce those delayed discharges – patients being kept in hospital when they shouldn’t be.”

Pressed further on cash, and whether extra money had, in fact, been offset by government cuts, Mrs May said: “You keep talking about the money but actually what you also need to look at is how the NHS works, how it operates.”

Shadow Health Secretary Jon Ashworth said: “She hasn’t got a plan to get those people off the trolleys and corridors.”